Prevention of sourness of sweet naphthas during distillation by distilling in the presence of an alkylene oxide and a salt of an organic acid



NoDrawing; Application November 7', 1955,

SerialNo. 545,530:

,1 1 8 Claims. (Cl. 196-25) This inventionrelates to therpreparation ofindustrial naphthas... ltis more specifically concerned with the UnitedStates PatennQ distillation of a sulfurecontaining, hydrocarbon mixtureseparated intovariousboiling ranges. Although highly aromaticpetroleummagihthas are readily available; the

subject. invention is only concerned with straight-run 3O ,petroleumnaphthas or equivalent hydrocarbonmixtures. Althoughfnaphthas consistessentially of mixtures. of low-boiling.hydrocarbons, there are presentin the, crude .oils fromwhichithese. hydrocarbon mixtures are derivedvarious-impurities, which arelretained in the distillates .rh-ir'in'g.theffractional distillation ofrthe crude. T he nature of. these.impuritiesvariesaand includes, amongothcrs organ'ic and,inorganic acids,nitrogen compounds, and sul fur compounds. Because-of the relativelyhigh-boiling .rauge of most of these materials, .they are found only inthewheavier petroleum distillates. However-{boiling 'within--the naphtharange are a number :of sulfur compounds whose presence is deleteriousbecause they impart to 'the' naphthadistillate certainundesirable. odorsas. well as .corrosiveproperties whichcause metal corrosion orjth'e'.darkening of ,paints' or varnishes. Specific applications of naphthacompositions, make it. necessary to refine naphthas vin order! to.control. their properties and insure "uniform quality. As was pointedoutin the definitionof a naphtha, naphtha preparation processesgenerally in; volve chemical refining followed by distillation of thechemically, treatediproduct. to produce naphthas haying a-selecte'clboiling range; Although refining processes are available, which removesubstantial amounts of 'ob-' noxious :sulfur compounds from admixturewitlr'hydroicarbons, these.processes..,generally. do. not reduce thesul- 'furnoontent sufficiently to eproduce a non-corrosive .and.

" substantially odor-free naphtha.- In the crefiningiofg petroleumi-anaphthas, processes referred to as: sweetening=' processes,areremployeqd in; which the objectionablel sulfur compoundgsuchasimercaptans, are converted or. trans-l formed into-acceptable ones 1without altering the sulfur content of the oil. I sulfu'r'compoundsfloes "not affect the usefulness of-the The presence of theless noisome naphthas as industrial products as long as these sulfurcompounds rarer non corrosive sand substantially. odorfree: Examplcsofsuitable; processes which areemployed. -':in' the fsweeteningiofslight-petroleum products .are the doctor-treat: usingasodium :plumbite,.the hypochlorite treatment, and treating-methods employing. copper-con-'tainingreagents -such as copperchlorideior. copper oxide.Qt'hensuitabIe :sweetening? processes are-comprehensive- Patented Dec.25, 1956 2 1y discussedby V. A. Kalichevskyin a series of articlesentitled sweetening-panda desulfurizationof light petroleum products,Petroleum Refiner, 30, (1951).

There are aivariety of processes which may be employed as thecomplementary fractionation step in the naphtha lpreparationprocess.In-some instances, such as the vapor-phasetreatment of petroleumdistillates with copper oxide-oil slurries, the :treated vaporousdistillate is reintroduced into lthercrudeoil distillation tower andrecoveredas .azconventional' side-stream cut. Other recover-yprocessesemploy special naphtha re.run units; in which the naphtha is.fractionated in a separate, fractionating system. Where particularlyclose. boiling-range fractions aredesiredwith a/minimum overlap ofboiling ranges, superfractionators havingna large number of plates areemployed. In units of this nature, due-to the height of-a columnnecessary toaccommodate the large number of plates, the column is splitinto two sections with the overhead from the first section passing intothe base of the second section. Reflux from-the second section isreturned to the top of the first section. Regardless of the combinationof'refining and distillation processes employed these sequential stepsoccur in naphtha preparationprocesses. As a result, it has been foundthat even 'though the'chemical refining step produces a naphtha freefrom objectionable sulfur compounds by converting them to relativelyinnocuousorganic sulfides or disulfides, the elevated temperatures"employed in subsequent distillation steps'cause the reconversion of theunharmful sulfur compounds into noxious sulfur compounds which arecorrosive and odorous; This problem is particularly prevalent in thepreparationof naphthas which contain components boiling above about 300F. However, this condition may also occur in the treatment of thelower-boiling naphthas because even though special designs are employedin order to avoid excess skin temperatures on the walls of thefractionation columns, high temperatures which facilitate the conversionof the organic sulfide or 'disulfides into undesirable sulfur compoundsfrequently are encountered. As a result, the naphtha products producedin this manner containing these obnoxious sulfur compounds do notconform to established specifications relative to the presence ofcorrosive and odorous sulfurcontaining materials.

A number of tests have been devised as criteria to determine the efiectof sulfur and sulfur compounds in naphtha. These tests, which arequalitative in nature,

include the copper strip corrosion test, the doctor test,

and the distillation corrosion test. This latter test is also vvariouslyknown as the Amsco corrosion test, the full flask distillation test, orthe-full-corrosion test. These .tests are standards in the petroleumindustry and are described in anaiticle ent tl f f sulfur n sulfurcompounds innaphtha upon ,certain corrosion tests, L. M. Henderson etal., Industrial and Engineering Chemistry,

Analytical-Edition; 1 2- l-),-1- et seq. The-distillation corrosion testis particularly severe as compared with other corrosion tests used inthe petroleum= industry, and there .is no correlation between theresultsof this test and'those of-other corrosion' te'sts; The naphthaproducts Whichin the courserof'the distillationstepare transformed intooff spec'ification products with regard'" to these tests, cannot berepurified by'a simple washing of the distillate with an aqueoussolutionloficaustic" soda and it is necessary to re-treat thecontaminated distillate inia 's'weetening (process; This, of course, isuneconomical and unsatisfactony refining practice. However, according tothis invention .it hasnbeen, founcl that by carrying out thedistillation step vin the presence of a stablizer, the undesirabledeterioration of the organic sulfides or disulfides is prevented. and.the development of the undesirable properties avoided. It istherefore anobject of this invention to provide a method for stabilizing sweetenedhydrocarbon distill-ates during distillation. It is another object ofthis invention to "provide a method for preventing the developmeut ofodor or eorrosiveness in sweetened petroleum liquids duringdistillation. These and other objects and advantages will be made moreapparent from the following detailed description of this invention.

According to this invention it has been found that if the distillationof a sweetened hydrocarbon mixture containing petroleum sulfurcompounds, including disulfides, is carried out in the presence of analkylene oxide and an oil-soluble basic salt of a high molecular weightorganic acid, not reactive with the alkylene oxide, a satisfactorynoncorrosive product as determined by the aforementioned test methodswill be obtained without requiring additional treating for the removalor conversion of obnoxious sulfurcompounds. The essence of the inventionis shown by the following illustrative but nonlimiting examples in whicha petroleum naphtha distillate was first sweetened by contacting thedistillate with an admixture of finely divided fullers earth and cupricchloride using the Linde Sweetening Process. The admixture was agitateduntil the petroleum distillate was made "doctor sweet. The sweetenedpetroleum distillate was recovered and separated into a plurality of 100ml. portions, which were then subjected to the standard ASTMdistillation test. Each distillation was carried out employing adifferent additive combination admixed with the distillate charged tothe distllaton flask. A series of 10 ml. fractions were taken for eachdistillate, each fraction being subjected to the scrutiny of the doctortest.

The data obtained in these distillations are listed in Table l. Thenaphtha which was treated was from a mixture of sour and sweet crudesand had the following characteristics Distillation I. ll. P. 5% 50% 95%E. P.

111 F. 136 F. 260 1?. 392 F. 414 F.

Sulfur distribution, percent weight Sulfur, total 0.077 Sulfur, free0.008 Sulfur, HzS None Sulfur, RSH 0.030 Sulfur, R252--- 0.004 Sulfur,RzS 0.028

um distillates. In these sweetening processes no correlation is requiredbetween the boiling range of the distillate being treated and theboiling point of the alkylene oxide treating agent. However, accordingto the instant invention, it has been found that in order to effectuatethe objectives of this invention, it is necessary to employ an alkyleneoxide having a boiling point at least as high as the end boiling pointof the naphtha fraction being distilled. This requirement is seen fromthe data in Table 1 wherein it is shown that neither ethylene oxide (B.P. 51 F.) nor propylene oxide (B. P. 95 F.) provides the advantages thatare obtained when an alkylene oxide, viz., dodecene epoxide (B. P. 520F.) having the aforementioned boiling point characteristics is employed.The data also shows that it is necessary to employ the combinationtreating agent of this invention as it is shown that the constituents ofthe composite, when used separately, are not effective.

The alkylene oxide which is added to the sulfur-containing hydrocarbondistillateprior to fractionation can be any alkylene oxide having aboiling point at'least as high as the end boiling point of the naphthabeing distilled. Specific examples of useful alkylene oxides include butare not limited to aliphatic alkylene oxides having suitable boilingpoints, as well as derivatives thereof, such as epoxides of unsaturatedfatty acid esters, e. g. methyl oleate; epoxides of unsaturated hydroxyacid esters, e. g. methyl ricinoleate; epoxides of unsaturated alcohols,e. g., 2-octen-l-ol; epoxides of unsaturated branched chainhydrocarbons, e. g. diisobutylene, triisobutylene and tetraisobutylene;epoxides of alicyclic olefins, e. g. u-pinene; epoxides of arylalkenes,e. g. styrene.

In carrying out this invention the amount of alkylene oxide, whichshould be present in the distillation zone while conducting thepreparation of the special naphthas will depend upon the amount ofsulfur compounds which are contained in the distillate undergoingdistillation. In treating conventionally sweetened petroleumdistillates, between about 1.0 to 3.0 weightpercent of alkylene oxidestabilizer should be used. The optimum quantity, however, should bedetermined experimentally by making tests on samples of the naphthawhich are to be subjected to processing in the distillation unit. Insome instances as much as 5% may be necessary but in others the presenceof amounts as low as 0.5% sometimes may be eifective.

The basic salt which is employed as an essential part 7 of thedistillation additive combination may be any oilsoluble basic salt of anorganic acid, having a positive base number, which is non-reactive withalkylene oxide S lfu id 0,007 and has a boiling point at least as highas the end boiling TABLE 1 Volume Percent Over 10 20 30 40 50 FirstDoetor Sour Run Material Added to Charge Naphtha Overhead Temperature atCut Point (F.) out Number Nona 144 169 196 214 235 250 275 286 334 7(250275) Ethylene Oxide 167 183 194 226 241 259 282 289 7 259-282) Bentoniteplus Ethylene Oxide. 151 212 250 270 284 304 322 7 284 304 2 m1.Dodecene Epxoide. 156 178 205 221 234 270 295 7 270-29 1.2 g. BariumSulionate 151 183 201 216 226 262 275 v 7 262-275 2 ml. Dodeeene Epoxideplus at m Sulfonate 158 189 205 230 255 271 309 329 356 363 9 329-3561.2 g. Barium Sulfonate plus Propylene Oxid 164 198 216 234 250 270 302324 352 6(250-270 Ethylene Oxide plus 1.2 g. Barium Sultan e 254 286 326349 375 6(254-286) 1 Basic oil-soluble barium sulfonate containing 12.7%ash as sulfate and having a 30 base number, prepared by sulionating amedium neutral oil followed by reacting the sulfonated oil with excessbarium hydroxide.

The tabular summary in Table 1 shows the various cut points at which thedistillate went ofl? specification with regard to the doctor test usedas the criterion and illustrates the unusualness of the instantinvention. The prior art in U. S. Patents 2,530,561 and 2,575,989discuss the efiectiveness of ethylene oxide alone or in combination withan alkaline catalyst for sweetening petrolerange of the naphthadistillate being fractionally distilled. This constituent is defined inthe appended claims as a basic salt of a high molecular Weight organicacid. The use of such oil-soluble basic salts constitutes an essentialpart of the subject invention because a uniform and completedistribution of the additive combination in the hydrocarbon fraction canbe effected, the hydrocarbon fraction is not subjected to contact withany extraneous immiscible alkali solutions which require subsequenttreatment steps, the unsatisfactory distillation of heterogeneousadmixtures produced by the presence of an aqueous phase is avoided, andminimum amounts of basic materials are employed. Examples of suitablebasic salts of highployed include sodium naphthenate, bariumnaphthenate,

sodium petroleum sulfonate, calcium oleate, magnesium stearate,potassium naphthalene sulfonate, etc. Salts of petroleum sulfonates arepreferred, especially barium and calcium salts.

In formulating the composite distillation additive of this invention theamount of .the basic salt employed will depend upon the character of theoil being treated, as well as the nature and concentration of the sulfurcompounds present. It is preferable to employ from about 1.0 to 5.0%, byweight, and preferably 1.02.0%, by weight, of the basic constituent,based on the naphtha. Although the illustrative examples of thisinvention describe the use of a batch-wise distillation process, theinstant invention may be carried out continuously. In the event that theformer technique is employed, the composite additive is admixed with thenaphtha charge and the distillation effected. It is preferred, however,that the distillation process be carried out continuously, in whichinstance the necessary amounts of composite additive may be introducedinto and admixed with the incoming feed.

Another important feature of the instant invention is illustrated by thecondition of the still pot after the batch distillation has beensubstantially completed. In employing the instant invention the residueremaining in the still pot even after about 95% by volume or more of theoriginal charge has been distilled is a clear, mild smelling liquid asopposed to the extremely odorous and adherent black solid material whichremains in the still pot after a conventional batch fractionaldistillation has been effected. Accordingly, the use of this inventioneliminates a cleaning and disposal problem of noxious still-pot residuesnormally remaining in a fractional distillation unit after asulfur-containing hydrocarbon fraction has been distilled.

The invention is broadly directed to the production of high qualitynaphthas and provides an improved method of distilling doctor sweetnaphthas whereby increased yields of higher boiling, sweet distillatesare obtained without further treating. Sweetened sulfur-containinghydrocarbon fractions boiling between about 100 F. and 500 F. may betreated in accordance with this invention. However, the invention hasparticular application in the treatment of straight-run, aliphaticpetroleum distillates boiling between about 100 F. and 400 F. Incarrying out the instant invention it is not necessary that thedistillation efliuent be further treated in order to provide asatisfactory non-corrosive product.

We claim as our invention:

1. Indie distillation of an oxidatively sweetened hydrocarbon fractioncontaining organic sulfur compounds, including disulfides, attemperatures normally effective for the conversion of said compounds toproduce doctorpositive products, the improvement which comprisescarrying out the distillation in the presence of sufficient amounts ofan admixture of an alkylene oxide having a boiling point at least aboutas high as the end boiling point of said fraction and an oil-soluble,basic salt of a high molecular weight organic acid to prevent saidconversion and the development of a doctor-positive distillationefliucut.

2. A distillation in accordance with claim 1 in which said basic salt isan alkaline earth metal sulfonate.

3. A distillation in accordance with claim 2 in which said basic salt isbarium petroleum sulfonate.

4. In the distillation of an oxidatively sweetened hydrocarbon fractioncontaining organic sulfur compounds, including disulfides, attemperatures normally eifective for the conversion of said compounds toproduce doctorpositive products, the improvement which comprisescarrying out the distillation in the presence of 0.5-5 by weight, basedon the charge of said fraction, of an alkylene oxide having a boilingpoint at least about as high as the end boiling point of said fraction,and 15% by weight, based on the charge of said fraction, of anoil-soluble, basic salt of a high molecular weight organic acid toprevent said conversion and the development of a doctorpositivedistillation effluent.

5. In the distillation of light petroleum distillate boiling betweenabout and 500 F., containing organic sulfur compounds, includingdisulfides, at temperatures normally effective for the conversion ofsaid compounds to produce doctor-positive products, the improvementwhich comprises carrying out the distillation in the presence of 0.5-5%by weight, based on the charge of said distillate, of anadmixture of analkylene oxide having a boiling point at least about as high as the endboiling point of said fraction, and 15% by weight, based on the chargeof said distillate, of an oil-soluble, basic salt of a high molecularweight organic acid to prevent said conversion and the development of adoctor-positive distillation eifluent.

6. A sweetening process for producing doctor-sweet petroleum naphthadistillate which comprises contacting a doctor-positive,sulfur-containing, light petroleum distillate in an oxidative sweeteningprocess under conditions to produce a doctor-negative petroleumdistillate containing organic sulfur compounds, including disulfides,distilling said doctor-negative petroleum distillate, at temperaturesnormally eifective for the conversion of said sulfur compounds toproduce doctor-positive products, in the presence of 0.55% by weight,based on the charge of said distillate, of an admixture of an alkyleneoxide, having a boiling point at least about as high as the end boilingpoint of said fraction, and 15% by weight, based on the charge of saiddistillate, of an oil-soluble, basic salt of a high molecular weightorganic acid to prevent said conversion and the development of adoctor-positive distillation efliuent, and recovering doctor-negativedistillate products.

7. A method for fractionally distilling an oxidatively sweetenedpetroleum naphtha containing organic disulfides susceptible todecomposition under distillation conditions which comprise fractionallydistilling said naphtha in the presence of 0.5-5 by weight, based on thenaphtha charge of dodecene epoxide and 1-5% by weight, based on thenaphtha charge, of basic barium petroleum sulfonate to prevent thedecomposition of said disulfides and the development of adoctor-positive distillation elfiuent.

8. In the thermal treatment of oxidatively sweetened hydrocarbonfractions containing organic compounds, including disulfides, attemperatures eifective for the decomposition of said organic compounds,the improvement which comprises carrying out the thermal treatment inthe presence of sufficient amounts of an alkylene oxide having a boilingpoint at least about as high as the end boiling point of said fractionand a basic salt of a high molecular weight organic acid to prevent thedecomposition of said organic compounds and the development of adoctor-positive distillation etfiuent.

No references cited.

1. IN THE DISTILLATION OF AN OXIDATIVELY SWEETENED HYDROCARBON FRACTIONCONTAINING ORGANIC SULFUR COMPOUNDS, INCLUDING DISULFIDES, ATTEMPERATURES NORMALLY EFFECTIVE FOR THE CONVERSION OF SAID COMPOUNDS TOPRODUCE DOCTORPOSITIVE PRODUCTS, THE IMPROVEMENT WHICH COMPRISESCARRYING OUT THE DISTILLATION IN THE PRESENCE OF SUFFICIENT AMOUNTS OFAN ADMIXTURE OF ANALKYLENE OXIDE HAVING A BOILING POINT AT LEAST ABOUTAS HIGH AS THE END BOILING POINT OF SAID FRACTION AND AN OIL-SOLUBLE,BASIC SALT OF A HIGH MOLECULAR WEIGHT ORGANIC ACID TO PREVENT SAIDCONVERSION AND THE DEVELOPMENT OF A DOCTOR-POSITIVE DISTILLATIONEFFLUENT.